In a stringed musical instrument, such as a guitar, the strings, placed under tension, extend unsupported between a first critical point usually formed by the nut positioned where the neck joins the head and a second critical point usually formed by a clearly defined point on the bridge positioned on the body. The strings are secured or fixed at one end on the body of the instrument to what is traditionally known as the tailpiece, strung over the bridge and extended past the nut at the transition from the neck instrument to the head, and, for conventional instruments, secured at the other end to the tuning pegs where an untensioned string is tensioned and adjusted to a tuned pitched condition, proper playing pitch for play, or, simply, tuned condition; sometimes a nut arrangement is provided for a headless or tuning peg-less design. The neck further comprises a fingerboard or fret board that a player presses the strings against to play various pitches up and down the neck; the fingerboard typically is formed with a convex radius that commonly varies between approximately 9″ and 16″.
The second critical point can be created as a part of a bridge or combined bridge and tailpiece structure. Traditionally, the size of the bridge element is quite small so as to create a clearly defined single point of contact between the string and the bridge element. It is between these two points that the playable string length is typically determined, sometimes referred to as the scale length or harmonic length. Adjusting the relative distance between the first and second critical points is called harmonic tuning or setting the intonation. Some bridges structures are individually adjustable, that is for each string, relative to the nut for achieving a more precise harmonic tuning. Usually this adjustment of the second critical point for harmonic tuning is carried out first and then the strings of the instrument are tuned to playing pitch. Often referred to the “initial setup”, it is not uncommon that further adjustment of the harmonic tuning is necessary for a variety of reasons, for example, including changing the brand of a string where the alloy of the strings is varied or when the gauge of strings the player chooses changes as well as “setting” the string by manually pulling on the string along the scale length in order to improve elasticity in the string at first tensioning before the string can confidently relied on to hold proper playing pitch during the life of the string.
Often the typical construction of the strings, particularly for guitar and bass, includes a plain end and, on the other end, a “ball end” which being a washer-like addition is wrapped by the string itself into a larger form to enable “fixing” or securing the string on the instrument to the tailpiece element; alternatives to the “ball end” include as known to those of ordinary skill in the art as “bullet ends” formed from metal and molded around the end of the string. The tailpiece is usually provides for an opening or recess sufficient in size to receive the strings of various diameters ranging from 0.007″ to 0.070″ or more while being smaller than the diameter of the ball end so as to limit the passing of the ball end through the opening or recess in order to secure or mount each of the individual strings to the body. The wrapping usually extends up to a ½″ towards the plain end and as such the position of the tailpiece structure relative to the bridge element must insure that the wrapping does not extend over the second critical point when arranged on the instrument; this wrapping, under normal circumstances, is not subject to stretch compared to the rest of the string. In the relevant art, “anchoring” strings is often referred to as attaching or securing a string and understood with the limitation that the anchoring is sufficient so that the string is fixedly attached or secured to the instrument under the typical tensioned conditions of the string that typically range from 16 to 20 lbs or greater. Stable fine adjustments of these and other elements have been a longstanding problem for stringed musical instruments.
Additionally, the popularity of guitars and other multi-stringed instruments having more than the typical 6 strings and/or using longer scale lengths, etc. are capable of a greater pitch range which creates the need for strings of a larger diameter. One solution is to utilize “taper core strings” that have one or two less layers of wrap near the “ball end” of the string to go over the bridge elements. Further, a “taper wound” string simply tapers away these layers of wrap as near the ball-end of the string, so the part that goes over the bridge has a smaller diameter. “Exposed core” strings taper down to the core itself, so the core goes over the bridge and lowers the action and increases sustain/resonance. These designs are often seen on B strings, typically a low string on a five string bass, for example. The logic is that a taper core string, etc. approach will help with intonating a larger diameter string. In some of these cases the strings are mounted to tailpiece portion by inserting the string through or over the bridge elements to avoid complications due to increased string diameter. The larger diameters can be problematic given the dimensions of vintage systems.
Playing pitch or proper playing pitch or pitched string condition is generally understood by one of ordinary skill in the art to be the pitch of a guitar string relative to the remaining guitar strings when a guitar is played “in tune.” For example, in a standard tuning arrangement, for a six string guitar, based on the standard A=440 Hz, the pitch of the 1st string (highest) is tuned to note E (329.63 Hz), the pitch of the 2nd string is tuned to note B (294.94 Hz), the playing pitch of the 3rd string is tuned to note G (196.00 Hz), the playing pitch of the 4th string is tuned to note D (146.83 Hz), the playing pitch of the 5th string is tuned to note A (110 Hz), and the pitch of the 6th string is tuned to note E (82.41 Hz).
In the Proelsdorfer U.S. Pat. No. 2,304,597, string tensioning devices placed on the tailpiece for fine tuning the pitch of the strings of violins, guitars and the like, were disclosed; such pitch adjustment is quite limited in range, comprising generally an interval falling between that of a whole tone and a major third at best, and designed to offer the tuning of the strings a minor adjustment of pitch after the general tuning is achieved with the tuning pegs on the head of the instrument which traditionally first provides for raising and adjusting the tension of the strings to pitch from an untensioned condition and then setting the string. This is regarded as fine tuning and the apparatus for doing so, the “fine tuners”, usually comprise an adjustment knob or thumb screw.
A familiar and very common traditional arrangement in many electric guitars comprises a thumbwheel supported bridge with moveable individual bridge elements for fine tuning the intonation or harmonic tuning for each associated string operable to adjust the height of the strings relative to the body and a separate tailpiece, often bar-like in appearance, supported by screws on each end, to secure the ball end of the strings such as the traditional Tune-O-Matic (“TOM”) and stop tailpieces from the 1950's, like found on Gibson branded musical guitars such as the Les Paul's, the SG's, the Explorer's, Flying V's, etc. in addition to semi-hollow body guitars in the ES lines as well as, are found on countless other guitars from other manufacturers. In this familiar configuration, two posts with integrated thumbwheels thread into inserts in the body to adjust the height of the TOM bridge whereas the stop tailpiece comprises a bar, transverse the direction of the strings, configured to receive two screws or bolts that mount the tailpiece within inserts to body. The two posts are now standardized in many cases with integrated thumbwheels centered about 2.925″ with the “bass side” set back about 0.125 relative to the nut and the tailpiece studs/inserts about 3.25″ apart and rearward of the bass side thumbwheel position by approximately 1.5″, although these dimensions still are often varied. Further, the TOM/Stop tailpiece arrangement, “4-post” setups provide at least 0.650″ distance from body to the intonation point on the lowest or first/sixth string, although historically, the dimension varied considerably.
It is known to those skilled in stringed musical instrument design and construction that various tremolos have been proposed and utilized for varying the tension of all the strings simultaneously for the purpose of creating a tremolo sound. Further, it is known to those skilled in the art that there are a great many commonly used names for such devices, such as tremolo, tremolo device, tremolo tailpiece, tremolo bridge, fulcrum tremolo, fulcrum tremolo bridge, fulcrum tremolo tailpiece, fulcrum tremolo bridge-tailpiece, vibrato, vibrato bridge, vibrato tailpiece, vibrato bridge tailpiece, etc.
In one specific species, known as the vintage or traditional fulcrum tremolo, first introduced in Fender U.S. Pat. No. 2,741,146 (“Fender '146”) shows and provides a device comprising a novel structure, which incorporates the bridge and the tailpiece. The portion supporting the bridge elements is called the bridge plate or the base plate. Further, both the bridge and the tailpiece elements connected to the base plate both move together as the fulcrum tremolo device is pivoted. In this archetype, the bridge elements and their corresponding intonation points or second critical point rotate around a single clearly defined axis, the pivot axis, the fulcrum axis, etc. Typically, in order to facilitate the fulcrum tremolo pivoting about its fulcrum axis, counter springs, as a biasing element, are utilized to counteract or counter balance the pull of the strings. Accordingly, a singular and defining aspect of the fulcrum tremolo is that the harmonic tuning is upset as the device is pivoted; and, accordingly, for an instrument equipped with a fulcrum tremolo, it is unique in that only restoring all of the strings to a proper pitched condition also simultaneously restores the harmonic tuning for all the strings. The base plate upon which the individual bridge elements are adjustably secured has a beveled ridge portion which is secured to the instrument body by six screws permitting pivotal movement about a fulcrum axis which varies the tension on the strings and produces the desired “tremolo effect”; in general, this device allowed for extensive dropping down of the pitch of all the strings and a modest upward capacity that further enabled the familiar mild pedal steel or Hawaiian guitar vibrato effect provided in gentle pivoting.
In this first vintage fulcrum tremolo, herein referred to as Type I, the metal bridge elements of Fender '146 are loosely held in place by a spring loaded attachment screw arrangement pivotally secured through openings in a small folded portion of the base plate farthest from the fulcrum axis. The bridge elements also incorporate set screws for varying the relative height of the bridge elements and, therefore, height of the respective second critical points relative to the base plate and by extension, to the body and neck.
The fulcrum tremolo is generally defined to have a base plate pivotally mounted to the body of the instrument and an “inertia block” or “tone block” or “spring block” that extends transverse the direction of the strings 90° to the base plate. The instrument body is fashioned to include a single body cavity comprising two distinctive sections. There is, first, an approximate 3.00″×1.00″, generally rectangular, transverse the direction of the strings, traditional “tremolo pocket” or “trem pocket” extending generally perpendicular from the top surface of the body to meet at 90° providing two approximate 3.00″ wide opposing faces, a first face closer the nut and a second face further the nut; and second the traditional, generally rectangular, approximate 4.00″×2.25″×0.775″ deep, cutout extending in the direction of the strings in the back of the instrument body, a “spring pocket”, to receive the spring arrangement. The spring block has a first surface closet the nut and a second surface, each surface generally perpendicular to the top of the instrument and generally parallel to the tremolo pocket first and second face. Although there are differences in specifications from one instrument manufacturer to another for the various designs of the fulcrum tremolos that are available, there is approximately 0.125″ to 0.250″ clearance, between the spring block and the tremolo pocket face closest to the nut, to provide for upward pitch change as the spring block pivots towards the nut. Counter springs are usually connected to the body of the instrument at one end and, on the other end, to, usually, a block of metal, milled or cast or a combination of the two, which being secured to the bottom of the base plate by three screws 90 degrees to the base plate, is often called a spring block or inertia block.
The typical spring arrangement includes, in addition to the biasing springs connected to the spring block, a “spring claw” to receive the first end of the biasing element, variably secured by two wood screws, to adjust the position of the spring claw relative to the body for a simple but cumbersome adjustment method. There is ample room for the spring block to pivot freely within the “tremolo pocket” cavity during use.
One of the most troublesome problems with prior art for the fulcrum tremolo has been maintaining the “initial position” achieved at “initial setup” when all the strings are brought to proper playing pitch as the harmonic tuning is achieved. When a musician plays on the string there is usually some kind of string stretch over time that results in the overall tuning, and thereby, the “initial position” going out of balance. Specifically, when the pitch of the string changes, the position of the fulcrum tremolo and the position of the second critical point relative to the nut changes which then instantly alters the harmonic tuning. This is especially problematic if a string breaks since the reduced force otherwise created by the tension of the broken string allows the entire tremolo to be subject to the known “backward tilt”, all the remaining strings are un-manageably sharp in pitch and the harmonic relationship to the fret placement and scale length is distorted, generally, to an undesirable degree. Furthermore, when the tremolo base plate tilts forward, the end of spring block furthest the base plate tilts away from the nut; and when the tremolo base plate tilts rearward, the end of the spring block tilts towards the nut.
This singular characteristic adds complexities in obtaining the primary goal of achieving a stable equilibrium, initial position, between the force of the tension provided by the use of biasing or counter springs (connecting between the tremolo and the body) in relation to the force of tension of all the strings (connected to the fulcrum tremolo and the end of the neck at the peg head by the tuning pegs or an optional nut arrangement that secures the strings without tuning pegs, etc.)
Accordingly, these and other inherences need to be addressed in achieving a true and lasting initial position for the fulcrum tremolo and which has been the object of many inventions. In this inherent inter-dependant system of tensioning forces, contrary to the requirements of other tremolo or fixed bridge arrangements, (in the ideal instance where the essential conditions of the initial setup have been established and the appropriate tensioning force of the springs provisioned), the precise tensioning to proper playing pitch for any less than the total number of strings will inherently fail to achieve pitch and harmonic tuning for all of those strings attached to the tremolo.
Often the pivot is subject to wear and the tremolo does not always return to its initial position. Great care is required to establish the initial position, since both aspects of adjustment are interactive for “floating tremolo setups”, and since it simultaneously provides both the proper harmonic tuning and proper pitch tuning for each of the individual strings in order to enable a lasting “initial setup”.
Therefore, for stringed musical instruments, as is known to those skilled in the art:                The second critical point is a clearly defined point on the bridge or individual bridge elements, the adjustment of which relative to the first critical point on the nut defines the length of the string or scale length and the adjustment of which is called harmonic tuning.        
For fulcrum tremolos as originated by Fender '146, when pivoted:                Both the bridge portions and the string anchoring means, the tailpiece, simultaneously move about a common fulcrum axis;        The harmonic tuning is upset and is only restored when all strings are at proper playing pitch;        The tuning pegs or other means of tensioning the strings are inter-dependant with each other in obtaining initial position; and        Various factors can disturb the equilibrium point between the tension of the strings and the tension of the counter springs and as a consequence disturb the initial position.U.S. Pat. No. 3,424,049, Nathan I. David, “Combined bridge, tailpiece and manual vibrato for guitars”, ('049) describes a multi-pivot axis spring steel element operable as a one-piece “cantilevered” combination flexing bridge and tailpiece for a tremolo:        A guitar attachment having manual vibrato comprising a bridge section for a connection to the guitar surface and combined with an integral tailpiece connected to the bridge. The tailpiece is not connected to the guitar surface but is cantilevered and is therefore free for substantially vertical movement.and        a simplified structure wherein a single strip of resilient metal is formed into a bridge section which is connectable to the guitar surface. Integral with the bridge section is a tailpiece which extends freely rearwardly in cantilever fashion. The guitar strings of course extend over the bridge and are locked, as usual in the tailpiece. A handhold bar is connected to the tailpiece. Accordingly, when the handhold bar is manually vibrated, the strings ends are lifted or rocked, resulting in alternate shortening and lengthening of the strings to produce vibrato when the strings are struck.Further,        Thus the combination structure comprises a flat, mounting or base strip 16 which is fastened to the guitar top face as by screws 17. A substantially vertical wall 18 (which is in fact slightly rearwardly inclined), integrally follows the base strip 16. Following wall 18 is the arcuately formed tailpiece 15, said tailpiece being concavo along its top surface so as not to contact 4.And        The combined base 16, wall 18, and tailpiece 15 are formed from a single piece of spring steel of an approximate thickness of 0.1 inch. The junction line of wall 18 and tailpiece 15 forms the highest line of the structure and thereby provides the bridge 22.        
Accordingly, David's bent piece of 0.100″ thick flat spring material, fashioned with four transverse bends, comprises bridge 22 by vertical spring area 15 to support the strings over the fret board and a tailpiece to secure that strings which flexes, when the tremolo arm is activated, to create the required effect. Further, since the flat spring material flexes at each individual bend that forms:                1) the tremolo arm support area,        2) the tailpiece element,        3) the bridge element as well as        4) to the connection point at the body,        
the arrangement, with its resultant four pivot axii, create an highly individual and complex motion and interrelationship of and between the bridge elements, the tailpiece and the body as the tremolo is activated.
Further, '049 has no provision for adjusting the intonation of each bridge element or the harmonic tuning or the string height relative to the body, etc. Accordingly, this inherent behavior does not meet the requirements, indigenous to the “fulcrum tremolo” as per original Fender '146, etc., that 1) the bridge elements and tailpiece each simultaneously rotate on an essentially singular pivot axis and each follow an essentially constant arc about the pivot axis, 2) the bridge elements are adjustably positioned relative to the body for individual height and 3) adjusted relative to the nut for harmonic tuning.
For those fulcrum tremolos equipped with fine tuners as with Rose U.S. Pat. No. 4,497,236, Storey U.S. Pat. No. 4,472,750 and Fender U.S. Pat. No. 4,724,737:                The bridge and tailpiece portions simultaneously move about the fulcrum axis when the device is pivoted for the tremolo effect;        The fine tuner screws simultaneously move with the bridge and tailpiece portions about the tuning axis when fine tuning; and        Fine tuners are designed to offer the tuning of the strings a minor adjustment of pitch after the general tuning is first achieved, typically, by the tuning pegs on the head of the instrument; and        Adjusting the tension of a string by the fine tuner knob alone simultaneously adjusts the harmonic and pitch tuning and can achieve tuning a string to proper pitch conditions while simultaneously achieving proper harmonic tuning.Improvements to the Fender '146 fulcrum tremolo have included Rose's “string clamps” at the nut, installed along with a “string tree” for some guitars, a horizontal bar positioned between the tuners and the “locking nut” arrangement, to facilitate stability and “string clamps” at a point on the opposite side of the intonation point or second critical point on each of the bridge elements relative to the nut in order to limit string stretch to the prime vibratory portion of the string within these two points defining the scale length.        
Knife Edge Pivots for the Fulcrum Tremolo
Rose (U.S. Pat. No. 4,171,661) adopts semi-circular shaped beveled edge to the base plate, called a “knife edge”, adjustably supported by two screw-like members, referred to generally as riser posts, positioned in the body to collectively improve the return to initial position after pivoting the fulcrum tremolo device. The knife edge fulcrum pivot arrangement provides for the base plate to be positioned generally parallel to the instrument body, often referred to as a “floating tremolo”, for example, and offered the novel possibility to substantively increase the tension of the string for upward pitch changes by rocking the base plate “rearward towards the body” with the arm. The inclusion of iterations of Fender '146, herein referred to as Type I, to include, similar to Rose, “the American Standard”, a knife-edge design on the leading edge, closest to the nut, of the base plate with a riser post arrangement adjustably connected to the fulcrum tremolo, herein referred to as Type II. In the American Standard string height is often close to 0.480 from the body and the bridge elements comprise an approximate 0.187 distance from the base plate to the intonation point or second critical point; additional height, including compensation for fingerboard radii is accomplished by set screws that displace the bridge elements from the base plate—although effective, this approach reduces coupling between the bridge and the base plate, and, in some case, unevenly since not all strings will require the bridge element adjusted off the base plate, etc. In Rose the starting height for the intonation modules is approximate 0.315 and varies to meet fingerboard radii requirements, etc., although the distance to the body varies considerably. In most instances, however, the height adjustment range is typically limited to less than 0.100″, demands to reposition the devices' range are usually are met by the design of the base plate itself, or the mounting method, etc.
These two vintage fulcrum tremolos of the last century, Fender and Rose in the 80's, are in part distinguished by the differing standards for the placement of the riser posts, that receive each of the knife-edges to create a pivot axis, relative to both first critical point on the nut as well as the second critical point on the bridge element. Accordingly, there are differences in the body pocket but less so for the cutout that receives the biasing springs and the distance from the face of the spring block nearest the nut to the corresponding face of the tremolo pocket.
Other solutions to creating a dependable pivot arrangement such as on the Marcus Caldwell (“Caldwell”), U.S. Pat. No. 7,297,851 B2 (the “'851 patent”):                A bridge assembly for a guitar having a bridge plate connected to an anchor plate by a single, horizontally positioned flat spring. The bridge plate has an opening that receives a portion of a sustain block. The sustain block has receptacles for receiving line tuners and string clamps.        
Here, Caldwell shows an alternative for the knife-edge/riser post arrangement with a single unbent flat spring 38 connected to the body 12 via bracket 32 on one end and base plate 90 the other end to create single reliable resilient pivot that is operable with the traditional biasing element/spring claw/adjustment screw arrangement of the 50's Fender Stratocaster. The flat spring is not pre-tensioned and exerts no biasing force on the tremolo from initial position in either direction; the arrangement relies on Fender's original spring block/spring/spring claw arrangement to bias the tension of the strings.
Enserink Innovation B. V. U.S. Pat. No. 5,522,297, “A Tremolo bridge for guitars”, shows “one or more expansion springs (155, 157)” being used to replace traditional the fulcrum tremolo spring arrangement in a knife edge/riser post arrangement.